Scandium may be included in the arc tube fill of a metal halide arc discharge lamp either as the halide or in elemental form. U.S. Pat. Nos. 3,351,798 and 3,979,624 disclose its use in halide form and U.S. Pat. No. 3,407,327 discloses its use in elemental form, while U.S. Pat. No. 3,577,029 discloses its use in either form and U.S. Pat. No. 3,911,308 discloses its use in both forms.